Where a workpiece is abraded with an abrasive sheet having an even abrasive layer without grooves, scobs from the workpiece get between the abrasive sheet and the abraded surface of the workpiece to disturb abrading it. Also, where abrasive particles fall off the abrasive layer of the abrasive sheet, the particles may flaw on the abraded surface by scratching. In prior art, several techniques have been devised to solve these problems. Amongst the techniques are providing grooves in the abrasive layer to collect scobs from the workpiece and abrasive particles fell off in the grooves to remove them. Prior U.S. Pat. No. 2,755,607 shows a technique which provides grooves in an abrasive layer to comb the abrasive layer. Such a technique, however, makes irregularity on edges of grooves combed, and makes masses of a binding agent to attach them to the teeth of the comb when the abrasive layer is combed by a certain distance. The masses fall off the teeth to attach in places on the surface of the abrasive sheet and make projections on it.
In another technique, various patterns of abrasive layers are made by printing on bases (see U.S. Pat. No. 4,142,334). Such an abrasive sheet has projections which are a pattern being an abrasive layer on a base, and grooves which are except projections. The technique is better for providing grooves, however, is inadequate to abrade and finish a surface of a workpiece to be a precise plane since planar precision of abrasive layers made by printing is not good. Abrasive layers made by printing are also peeled off bases easily.
In another technique, abrasive layers are attached only on tops of projections in bases made of foaming plastics preprovided grooves in (see U.S. Pat. No. 4,111,666). The technique is also better for providing grooves, however, is inadequate to finish a surface of a workpiece to be a precise plane since abrasive layers are not attached evenly on edges of projections.
Furthermore all of above techniques providing grooves have intricate processes of making.
It is accordingly an object of the present invention to provide an abrasive sheet with irregularities with better planar precision of abrasive layers hard to be peeled off bases, said abrasive sheet being made by a relatively simple method.